1. Field of the Invention
The present invention relates to radial tires and more particularly to radial tires in which the durable life is noticeably improved by highly improving corrosion fatigue resistance of steel cord reinforcing materials embedded in rubber.
2. Description of the Prior Art
Prior radial tires reinforced with steel cords have had drawbacks that when these tires are used under corrosive atmosphere, steel cords are corroded, the fatigue resistance of the cords is lowered, the adhesion of steel cords to rubber is reduced and the steel cords are broken and the radial tires cannot be used.
As the cause of causing corrosion, it has been considered that tires are subjected to outer damage and rain water permeates from the outer damages, water remains between a tire and a tube when a tire is mounted on a rim and said water permeates through an inner liner of the tire and a corrosive gas is evolved when tires are vulcanized or run.
A variety of studies have been heretofore made with respect to this problem. For example, Japanese Patent Application Publication No. 24,626/77 has disclosed that a corrosion preventing lubricating oil for metal wire consisting essentially of an ester prepared from benzene tricarboxylic acid and an alcohol having 6-16 carbon atoms or an ester prepared from a fatty acid having 5-24 carbon atoms and a monohydric alcohol having 1-10 carbon atoms is previously applied on steel cords. Japanese Patent Laid-open Application No. 10,454/81 has disclosed that a protective layer of a corrosion preventing agent comprising of a surfactant of benzotriazol derivative, etc. and a film-forming agent (consisting essentially of a hydrocarbon polymer having a softening point or melting point of higher than 50.degree. C.) is applied on steel cord surface.
These processes comprise only applying a slight amount of such treating agents on steel cord surface, so that said agents are removed by rubbing of steel cord filaments due to the input in flow of rubber during vulcanization of tire or when running of tires and the satisfactory corrosion preventing ability cannot be yet obtained.
Japanese Patent Laid-open Application No. 90,692/80 and No. 43,008/81 have disclosed that the twist structure of the steel cord filaments is improved aiming that an embedding rubber composition is fed into the inner portion of steel cords and the inner portion of the cords is completely filled with the rubber composition, whereby the permeation of water is prevented. However, this process is limited in the applicable cord structure and it is impossible to completely feed rubber into the inner portion of the cords and therefore water partially permeates and rust is formed in the steel cords and the expected effect cannot be obtained.